Regrowth crops play role in spread of poppy disease

Published: 14 Sep 2018

In 2014, much of Tasmania’s poppy crop was threatened by the devastating systemic downy mildew disease which sparked a rapid response research initiative led by the Tasmanian Institute of Agriculture. Four years later, research is continuing to provide growers with strategies for reducing the impact of the disease.

“Growers are more conscious about sticking to rotations and this is helping to reduce the spread of the disease. Rotations of poppy crops should be a minimum of three years, but I would actually recommend at least five years, as we’ve taken soil samples that have picked up mildew in soils that haven’t had poppies for four years,” Dr Scott said.

Dr Scott said systemic downy mildew spreads through contaminated seeds, soil and airborne spores. A new focus of the research is capturing and analyzing airborne spores in an effort to better understand the spread of the disease and provide growers with effective management strategies.

“Last season we started trapping airborne spores for the first time, with traps established on commercial farms at six locations around the state including Bothwell, Cressy and Sassafras. Samples were collected from these sites on a weekly basis and a DNA extraction was conducted back in the lab,” he said.

“We know that airborne spores can potentially travel tens to hundreds of kilometers on the wind and we want to gain a better understanding of how they are moving around the state and whether this occurs in some regions before others.”

Upon analysing the data, Dr Scott was concerned to find that low levels of spores were being picked-up before poppy crops had been sown, indicating that contamination from the previous season’s regrowth crops was a big issue.

“Even if you start with very clean seed and a paddock that has never had poppies in it, airborne spores can still blow in and infect the crop,” he said.

“We recommend that growers get rid of regrowth as early as possible so that spores don’t go on to infect new crops. This is also important help reduce soil borne inoculum, so the benefit to growers is twofold. If a paddock is at risk of infection from nearby regrowth, then earlier fungicide applications would be more effective, so it is best for growers to discuss this option with their field officer.

“The highest spore loads we detected last year were during November to December which is what we would expect as during this period the crop is doing the majority of its growing. Unfortunately, this also gives the downy mildew more leaves to form spores on.”

The airborne spore trapping project will continue for another two growing seasons, giving the research team a more rigorous and long-term understanding of how spores move around the state.

Dr Scott said a future output from the project could be the development of a monitoring system that provides growers with warnings when an increased level of spores are prevalent, helping them to make informed management decisions about the timing of fungicide sprays.

The research is part of a $1.6 million Australian Research Council Linkage Project ‘Development of a risk management system for systemic downy mildew of poppy’ and is a collaboration with the Tasmanian Government, Poppy Growers Tasmania, SunPharma Australia and Tasmanian Alkaloids.

TIA is a joint venture of the University of Tasmania and the Tasmanian Government.